I will give my 2 cents here…
For me (and I think that some developers also feel that way), it is not the fact of a new feature that is being built that I don’t need that bothers me, but it is that sometimes I never saw that feature being highly requested by users at all (using the Corona Feedback system as my guidance)…
So, in summary, I think it is more something related to lack of transparency / alignment of expectations…
I understand that Corona needs sometimes to develop specific features under a stealth mode, but I really think that the number of complains would dramatically decreases with Corona provide the developers with the pipeline of features being/to be developed in the next 1/3/6/12 months or something like that…
About the marketplace, it don’t know if it is technically difficult to implement, although I understand that commercially speaking it can be tricky… But even if it is technically difficult, it is something that would benefit not only the Developers but specially Corona since a lot of new features that are requested to Corona would be developed by others, releasing Corona manpower to develop new core functionalities/products.